Generally, foodstuff casings are made either of natural material such as cellulose or animal guts, or of synthetic material. Usually, the foodstuff is packed into the casing. When smoked products are desired, the encased foodstuff can be further subjected to a smoking process. In a conventional smoking process, the product is suspended in a chamber wherein it is exposed to hot smoke from burning wood. This process has the disadvantage that only natural casings can be used in this process, that is, those obtained from guts, for example, or cellulose or collagen casings which all show a natural permeability to smoke.
A critical point in the preparation and storage of smoked products is that the casings must show different permeabilities depending on the step of the process. A high permeability is needed at high temperatures (typically between 50 and 100° C.) and high humidity, during the smoking process. Typically, the highly permeable cellulose casings and fibrous casings (which are cellulose casings re-inforced with wood fibers) have moisture vapor transmission rates in excess of 1000 g·25 micron/m2·24 hrs. Once the product is smoked and cooled, it is preferable that the casing acts as a barrier against humidity so the permeability should preferably be low, that is at rates below 1000 g·25 micron/m2·24 hrs, at temperatures less than 50° C., particularly less than 30° C. Depending on the specific application, the desired permeability at temperatures less than 30° C. could be substantially below 1000 g·25 micron/m2·24 hrs.
Casings made from natural products and/or cellulose can present many disadvantages: they can be expensive; their great permeability to steam can cause significant weight loss from a foodstuff; the product can be unstable due to drying and/or superficial fat oxidation. Also, graying caused by microbial spoiling of the natural casing often appears on casings. The manufacturing process for fibrous and cellulose casings involves emissions of carbon disulfide and hydrogen sulfide to the atmosphere, which can be an environmental concern, or require expensive gas scrubbing systems to minimize emissions.
There have been different approaches which attempt to overcome these problems. Single and multilayer plastic casings for packaging sausages are known in the art, for example. Recently, developments have been described in PCT Patent Application Publication WO 02/054878 to make polyamide-based casings more smokeable by blending in absorptive polymers.
Traditional smoking processes also can be inefficient in the absorption of the smoke flavorants and coloring relative to the amount of smoke produced in the smoking chamber. To try to overcome the disadvantages of the traditional smoking processes, smoke can be passed through water to prepare a concentrated solution of flavorants and colorants absorbed from the smoke, and such a solution can be used as a food processing material. This “liquid smoke” can be applied to the foodstuff during the curing process to flavor and color the foodstuff. Typically liquid smoke is applied to the surface of the food product by showering, atomizing or spraying. However, unless the liquid smoke is maintained in good contact with the surface of the foodstuff during the cooking process, use of liquid smoke is still relatively inefficient—more liquid smoke is lost than is applied. In addition, liquid smokes tend to be corrosive, and if not applied properly, cause inconsistent color and flavor.
A commercial practice for using liquid smoke involves laminating a special paper product onto a cast multilayer film of polyethylene and polyamide, and then converting the film into a tubular casing with a special sealing strip at the seam. Liquid smoke is then applied to the paper layer for transfer to the foodstuff during the cooking process.
U.S. Pat. No. 5,382,391 describes a thermoplastic film containing a modifier, such as liquid smoke, which can be transferred to the outer surface of meat during cooking. The inner layer of the thermoplastic film is a nonabsorbent polyolefin polymer such as an ethylene vinyl acetate copolymer or polyethylene in which is blended with 15 to 40 wt % polyethylene oxide.
U.S. Pat. No. 5,382,391 describes an edible collagen food wrapping containing liquid smoke encapsulated within an ingestible lipid or other oil-soluble fatty acids or waxes, where the liquid smoke is released during curing or cooking, and prior to consumption of the collagen-enclosed food product.
However, none of the conventional processes are trouble-free. It can be desirable to have a synthetic casing that can be used effectively and efficiently for storage and for a smoking process utilizing liquid smoke.